Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Jeffrey Hayat]

Hi - sorry if this has been covered before; a search revealed nothing.

Is there a maximum length that you can run an XLR/Mic cable from mic to pre? If so, what is it, and what to do if you need to go further?

Thanks in advance

[Mike Cleaver]

I try never to go more than fifty feet.
If you need an extremely long run, put the preamp close to the mic (within 50 feet)  and run the line level out to your destination on shielded balanced cable.

[Klaus Heyne]

And 50ft. is really the max, as far as I have tested.

Also try to not run mic cable into patchbays with further mic-level cables after the patchbay. It's always a good idea to bump up to line level (i.e. output of mic pre) as soon as you can.

[studiochap]

Klaus Heyne wrote on Sat, 17 October 2009 02:43

Also try to not run mic cable into patchbays with further mic-level cables after the patchbay. It's always a good idea to bump up to line level (i.e. output of mic pre) as soon as you can.

Absolutely - we've been revamping the 1970's Ronnie Lane LMS mobile for the last year or so, and very early on I took the decision that the mic lines weren't going anywhere near a patchbay. Also in my experience the normalling on patchbays can give hassles with the phantom power, as well as with the balanced audio signal, and you just can't risk it. Also use good quality cable between wall box and console -too many studios use cheap multicore that's more suited to line level signals ...( not to mention mic cables that are of less than optimal quality....)

As far as the mic pre thing goes, back in the tape days I would have a V76 literally at the bottom of the vocalist's mic-stand , with the output going straight to the tape track, (or via a U73b). Nothing to lose sonically, and everything to gain by keeping the mic leads as short as possible.

[yoink]

Some good points. What do you two think about using a straight-through XLR patch panel? I had installed one to keep from pluging cables into the back of the mic pres, but they're not patch bays (no normaling - just in to out hard wired) just mic to panel (never more than 25ft cable) and then panel to pre (3 foot cable).

[studiochap]

yoink wrote on Sat, 17 October 2009 05:18

. What do you two think about using a straight-through XLR patch panel?

That's exactly what we've done with the LMS mobile.

[Schallfeldnebel]

I have used over 300ft without problems. Often I have no choice, that's the length it takes to the control room, and it's not always possible to have microphone preamps on stage, e.g. live broadcasts.

[compasspnt]

I generally agree with The 50 Ft Rule, but admit to having used 200+ ft when no other choice, and it worked at least...

[Jeffrey Hayat]

I appreciate all of the responses - thank you.  

I am going to be doing some recording in a concert hall, and wanted to put my computer/preamp in the back, so the noise will not be picked up by the mics. I am going to have some mics on stage (not a problem length-wise there), but also some towards the middle of the hall to capture the ambiance - it is those mics I am concerned with. Good to know that I can work with 200 ft.

Cheers.

[Plush]

I am trying to address the OP's question here.

There is really no problem with running very long mic lines and this is confirmed by the recording scientists who do the research.

Neumann themselves have technical papers showing no degradation when running 250 to 300 feet. We commonly do this length run.
Gotham cable, Sommer cable and the Austrian and Swiss cables makers have also done the same research.

Going much beyond this distance is OK if you can stand to suffer high freq. losses and the increased chance of picking up RF interference.

Indeed measuring high frequencey loss in microphone cables shows perhaps a -1 dB loss at 20KHz. somewhere after 400 feet.

The longer the run, the more one is open to having your cable turn in to an antenna and pick up RF interference.

Keeping mic lines short is always good practice but a 50 foot rule noted here is strictly an arbitrary distance.  

[David Satz]

The answer depends on the capacitance of the cable as well as the output impedance of the microphone. For their microphones with output transformers, Neumann has specified for decades a maximum cable length of 300 meters--and that's with the output transformer in the standard 150 or 200 Ohm setting. To avoid the loading effect of long cables it is far better if the output transformer is set at its lowest-impedance setting--generally 50 Ohms--and if the cable doesn't have unduly high capacitance between its modulation leads. (Some well-known Japanese star-quad cable falls into that category, unfortunately.)

Transformerless microphones can have even lower output impedances, and usually the character of that impedance is primarily resistive within the audio range. Thus even the 300-meter limit doesn't apply to them unless cable with extremely high capacitance is being used. But this forum isn't exactly teeming with fans of transformerless microphones, so I'll simply quote from Neumann's manuals for their fet 80 microphones, most of which contain either this exact text or something very much like it: "The cable length between microphone and amplifier should not exceed 300 m (980 ft.). The capacitance of greater cable lengths could affect the frequency response and, in conjunction with the leakage inductance of the microphone's output transformer, would result in a rise at the upper end of the frequency range."

--best regards

[jrmintz]

How about ribbon mics? I frequently run a Royer SF-12 through a 100ft Gotham cable. I don't hear any degradation, but it's not possible to do a comparison in the situation I'm using it.

[David Satz]

The Royer models that don't have built-in electronics have somewhat higher output impedance than studio condenser microphones are supposed to have--300 Ohms, except around their primary resonance at low frequencies where the impedance exceeds 1 kOhm (!)--and they are correspondingly more sensitive to the effects of longer cables and/or preamps whose input impedance is lower than it should be. With their lower sensitivity, their signals are also more susceptible to interference.

So for these mikes (which I've used, and like very much) I'd suggest keeping the cables reasonably short, avoiding the use of any high-capacitance cable, using Neutrik "EMC"-series plugs on the cables, and making sure that the preamp's input impedance is well above the usual 1000-1500 Ohms if at all possible.

--best regards

[AlexVI]

As another undertaking most recording on location, I can happily agree that lengthy runs have not presented me with any difficulties as yet. I've rarely needed to go more than 50m-60m, but on occasion up to 100m (some Cathedral naves are extremely long, especially  once the cable is run round edges in a safe manner), and I've not yet perceived a lack of quality in the signal coming down that cable.

AVI

[Mark Lemaire]

I also must weigh in that my location recording service uses 100' and 130' cables as a matter of course. While some exacting customers/ clients have spec'ed that the preamps be onstage and runs to the control room be at line level I have never had problems with putting the preamps in the CR.

That isn't to say that there is NO improvement in shorter cable runs- every little detail counts towards a great product. But this has not been my priority-- my more immediate concerns have been elsewhere.

However: the idea of 300 meter cable runs puts me ill at ease. It's nice to know that the science boys have at least approved it.

The issue of patch bays and interconnects is, I think a related but a very different issue. I try to keep the cable run simple and with as few connectors as possible as the connectors are the point at which screwups and bad solder joints occur. Mic straight to preamp with one cable is my objective.

[Klaus Heyne]

Mark Lemaire wrote on Tue, 10 November 2009 22:54

However: the idea of 300 meter cable runs puts me ill at ease. It's nice to know that the science boys have at least approved it.

Don't giv'em too much credit. Sometimes we forget the abysmal state of measurements in our business. The science boys have been known, on occasion, to shamelessly and ignorantly lean on the term "scientifically proven" with less than respectable real-world results.

Remember the scientific "lamp cord is as good as anything" test by the Nagra fella in San Francisco, in the 1980s?

[drknob]

I have installed higher capacitance star quad cable in mission critical environments like scoring stages. Sometimes the additional noise immunity of the cable is worth the small reduction in HF performance. In one case, we also had some low capacitance lines available for those sensitive to this issue.